In Multiple-input and multiple-output (MIMO) multiple antennas are normally used at both the transmitter and receiver to improve the performance of radio communications. In a MIMO system vertically and horizontally polarized dipole antennas may be used to receive and/or transmit vertically and horizontally polarized electromagnetic waves, respectively. In theory the use of two dipole antennas, one horizontal and one vertical should allow for successful recovery of vertically and horizontally polarized signals. However, the combination has proven less than ideal under real world conditions encountered by mobile wireless devices.
Some of the problems with the use of dipole antennas can be appreciated from the diagram of FIG. 2 which shows the azimuth directivity pattern 16 for a horizontal dipole antenna such as the antenna 10 shown in FIG. 1. While the directivity pattern of a vertical dipole antenna is omni-directional in the horizontal plane, the corresponding pattern of a horizontal dipole varies considerably with the angle of incidence, as shown in FIG. 2. Note that the horizontal dipole cannot receive or transmit a wave from or in the direction it is pointing to as illustrated by the presence of nulls in the antenna pattern. Given the limitations of the dipole antenna in the horizontal direction, a successful transmission and/or reception operation may require the user and/or some mechanical apparatus, to orient the horizontal dipole in such a way that its broadside points to the direction of the receiver/transmitter device with which communication is attempting to be achieved. It should be appreciated that this approach is not very user friendly and can be relatively expensive when the rotation processes is implemented using a motor or other automated process.
In view of the above discussion, it would be desirable if improved methods and apparatus could be developed to provide antenna diversity in terms of both horizontal and vertical polarized antennas being supported but without the need to rotate or otherwise mechanically reorient a dipole antenna to achieve suitable reception/transmission characteristics relative to the position of another device with which communication is being attempted.